[Specification] Add creation, deletion, reconnect, DnD and labels specification for all elements of each diagrams.

For each diagram, the specification shall describe the element creation behavior, the drag and drop, the reconnect and the deletion behavior, and also describe how the label is computed.

Specifications shall be available using help at the same level than User and Developer documentation. Diagram specification Activity diagram specification Class diagram specification Communication diagram specification Component diagram specification Composite Structure diagram specification Deployment diagram specification Package diagram specification Profile diagram specification StateMachine diagram specification UseCase diagram specification